effects of wetting and drying on carbon and …
TRANSCRIPT
EFFECTS OF WETTING AND DRYING ON CARBON AND NITROGEN
MINERALIZATION IN SELECTED COASTAL PLAIN SOILS
by
JOHN SAYLER KRUSE
(Under the direction of David E. Kissel, Ph.D.)
ABSTRACT
Carbon and nitrogen mineralization from soil organic matter are important components of nutrient cycling and crop nutrient availability. The objective of this study was to determine effects of repeated wetting and drying of soils on rates of C and N mineralization. The study compared mineralization rates in three soils, utilizing cotton leaves or compost residues. One set of treatments was subjected to repeated drying and rewetting and the other was kept at constant moisture content. Rates of C mineralization were measured in the treatment containers. Mineralized N was measured by leaching with 0.01 M CaCl2 periodically, for 185 d. Carbon mineralization rates were not significantly affected by moisture regime. Both residue and soil type affected rates of C mineralization. For N mineralization, moisture effect was not significant in control soils with no residue, but did significantly affect mineralization from residue. INDEX WORDS: Carbon mineralization, Nitrogen mineralization, Wetting and drying, Crop residues
EFFECTS OF WETTING AND DRYING ON CARBON AND NITROGEN
MINERALIZATION IN SELECTED COASTAL PLAIN SOILS
by
JOHN SAYLER KRUSE
B.S.A., The University of Georgia, 1986
A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial
Fulfillment of the Requirements for the Degree
MASTER OF SCIENCE
ATHENS, GEORGIA
2002
© 2002
John Sayler Kruse
All Rights Reserved
EFFECTS OF DRYING AND WETTING ON CARBON AND NITROGEN
MINERALIZATION IN SELECTED GEORGIA COASTAL PLAIN SOILS
by
JOHN SAYLER KRUSE
Approved:
Major Professor: David Kissel
Committee: Miguel Cabrera Paul Hendrix Electronic Version Approved: Gordon L. Patel Dean of the Graduate School The University of Georgia July 2002
iv
DEDICATION
This thesis is dedicated to my wife, Lyn, and to my children Johnny, Katie, and
Noah Kruse. Your patience and understanding, as well as your prayers, made this
possible. God bless you.
v
ACKNOWLEDGEMENTS
I would like to express my special thanks to Dr. David E. Kissel, my major
professor, for his oversight and insight in helping me complete this thesis. Without his
continued support and encouragement, this project would not have been successful. I
also express my deep gratitude to Dr. Miguel L. Cabrera for his tireless patience through
my endless questions, and his immense help in analyzing the data.
Over the past two years many other people have assisted in different aspects of this
project. I would like to mention Autumn Weaver, who kept me from “wigging out” over
the little things and has been a great friend. Thanks to Dr. Feng Chen, who kept my
computer from turning against me, and to John Rema, for allowing me the use of his
laboratory and all his helpful advice. Much appreciation is extended to Wick Johnson for
the nitrogen extractions.
vi
TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS.................................................................................................v
TABLE OF CONTENTS................................................................................................... vi
LIST OF TABLES........................................................................................................... viii
LIST OF FIGURES ........................................................................................................... ix
INTRODUCTION ...............................................................................................................1
LITERATURE REVIEW ....................................................................................................4
Introduction..................................................................................................................4
Effects of residues, soil texture, and soil organic matter on N mineralization ............4
Effect of moisture on C and N mineralization .............................................................8
Effect of wetting and drying on C and N mineralization...........................................10
Carbon and nitrogen mineralization rates based on microbial biomass response
to repeated wetting and drying ..................................................................................12
Compost and leaf litter in C and N mineralization ....................................................14
CHAPTER 1. PRELIMINARY WORK TO STUDY THE EFFECT OF DRYING
ON C AND N MINERALIZATION .................................................................................18
Introduction................................................................................................................18
Materials and Methods...............................................................................................18
Results and Discussion ..............................................................................................24
vii
CHAPTER 2. THE EFFECT OF WETTING AND DRYING ON NITROGEN
MINERALIZATION .........................................................................................................29
Introduction................................................................................................................29
Materials and Methods...............................................................................................29
Results and Discussion ..............................................................................................33
CHAPTER 3. THE EFFECT OF WETTING AND DRYING ON CARBON
MINERALIZATION .........................................................................................................47
Introduction................................................................................................................47
Materials and Methods...............................................................................................47
Results and Discussion ..............................................................................................52
REFERENCES ..................................................................................................................60
viii
LIST OF TABLES
Table 2.1 Soil particle size distribution, C and N concentration, C to N ratio, and
initial inorganic N concentration ...............................................................................39
Table 2.2 Dry weights, total C and N concentration, C to N ratio, and initial inorganic N
concentration of cotton leaves and compost ..............................................................40
Table 2.3 Net N mineralization after 185 days of incubation for the three study soils and
treatments...................................................................................................................41
Table 2.4 GLM Table for N mineralized as % N applied as residue. α=0.05 ...................42
ix
LIST OF FIGURES
Figure 1.1 Loss of water content in Orangeburg and Norfolk soils in chambers
maintained at 98% and 50% RH................................................................................26
Figure 1.2 Cumulative % Cl- recovery from coastal plain soils in 50 mL aliquots...........27
Figure 1.3 CO2-C evolved from coastal plain soils over 165 hours, as measured by
infra-red gas analyzer (IRGA), to determine initial rates of CO2-C evolution
from soils with incorporated residues ........................................................................28
Figure 2.1 Cumulative N mineralized from the control soils with no residue...................43
Figure 2.2 Nitrogen mineralized as % of N applied as cotton leaves or compost
under different moisture regimes ...............................................................................44
Figure 2.3 Plot of least squared means x moisture ............................................................45
Figure 2.4 Total soluble C extracted from Norfolk soils with cotton leaves to
evaluate whether treatments that underwent repeated wetting and drying
experienced denitrification.........................................................................................46
Figure 3.1 Total mean integrated CO2-C after 185 d from the three selected soils at
various combinations of moisture regimes and residue types ...................................57
Figure 3.2 Mean cumulative CO2-C in the three control soils with no residue applied,
by moisture regime ....................................................................................................58
Figure 3.3 Cumulative CO2-C, evolved from cotton leaves or compost, by moisture
regime ........................................................................................................................59
1
INTRODUCTION
The spatial variability of soils in crop production fields makes it difficult to predict
chemical and biological processes due to variations in soil properties such as organic
matter, clay content, water content, and available nutrients. These factors may influence
the rates of C and N mineralization to a significant degree.
Despite the difficulty in predicting mineralization, much research has been
conducted to develop an accurate predictor of mineralization. There are good reasons,
both economic and environmental, to predict C and N mineralization correctly. In a
study by Cabrera and Kissel (1988), mineralized N varied from 31 to 51 kg N ha-1 on a
conventionally tilled soil, and from 21 to 107 kg N ha-1 in a fallow field over 127 days in
May through September. This may represent a substantial portion of the nitrogen needs
of a crop over a growing season. Better knowledge of actual mineralization rates would
allow a producer to forego the expense of purchasing and applying surplus N.
Additionally, concern has increased dramatically among the scientific community over
human influence on the global N cycle. World N fertilizer use increased from 10 Tg yr-1
in 1960 to 80 Tg yr-1 in 1990. A tally of world crops revealed only 53 Tg N were
harvested in 1990, indicating only 2/3 as much N was harvested as was applied. This
excess N can become a source of groundwater and stream contamination (Frink et al.,
1999).
A more thorough understanding of the factors that influence both C and N
mineralization should lead to N fertilizer applications that better reflect the actual needs
2
of the crop. This process would begin with determining the N needs of the crop based on
expected yield, calculating the amount of N that will be available from mineralization
over time and space, then subtracting mineralized N from the crop N needs to determine
the N fertilizer required. The nitrogen available from the soil depends on the initial
available soil N, the type and quantity of crop residues returned to the soil, N added from
rainfall, as well as N losses from volatilization and leaching (Neeteson, 1990). One
obstacle to the aforementioned method is the fact that mineralization is primarily
biologically driven. Often temperature and moisture factors cannot be controlled even
though they have a profound influence on C and N mineralization rates (Birch, 1958).
Repeated wetting and drying, as occurs in the field, may have a pronounced effect
on mineralization rates. As soil water content reaches wilting point microbial activity
decreases (Stark and Firestone, 1995). However, when a soil is rewetted microbial
activity, as measured by respiration, begins again in a few hours (Lundquist et al., 1999).
Rates of mineralization are highest soon after a soil is wetted to field capacity (-0.01
MPa), then taper off over time. Soils with frequent drying and rewetting cycles exhibit a
decrease in the magnitude of the flushes over time due to a depletion of the organic
reserves (Birch, 1958).
The objective of this research was to quantify the effect of wetting and drying on
mineralization of C and N from soil organic matter, and from decomposing organic
residues incorporated into the soil. While many previous studies have indicated the
importance of soil moisture levels as a factor in C and N mineralization, they often
maintained the incubations at constant moisture levels throughout the study. It was
hypothesized that the wetting and drying cycles would increase net C and N mineralized
3
over a control maintained at constant moisture. The concept was to more accurately
reflect actual field conditions that are subject to periodic rain episodes interspersed with
periods of drying.
Soils selected for this study were obtained from an agricultural production field that
is conventionally tilled. The soils differed in clay and organic matter content, since these
factors vary widely and may influence mineralization. Cotton leaves were included in the
study at a rate that approximately reflects field residue amounts. A compost was also
incorporated into the study to provide a contrast to the cotton residue. Many
municipalities and companies throughout the United States are composting organic
materials from municipal wastes. Compost may become an increasingly available source
of organic residue in the future.
4
LITERATURE REVIEW
Introduction
Decomposition by microorganisms is the primary means by which organic carbon
and nitrogen are converted to inorganic forms in the soil (Tisdale et al., 1999). Factors
that influence the population growth, mobility, nutrient consumption, and respiration of
these microorganisms have a direct effect on the rates of C and N mineralization. Studies
reveal that the environmental factors: moisture, temperature, pH, oxygen, and soil
properties, affect C and N mineralization rates to differing degrees.
Effects of residues, soil texture, and soil organic matter on N mineralization
Other than N fertilizer, decomposing crop residues and soil organic matter typically
represent the single largest source of mineral N that is utilized by a crop. Determining
and predicting N mineralization rates based on crop residue quality and quantity has been
the subject of many previous studies. In a study of leguminous crop residues in soil,
Frankenberger and Abdelgamid (1985) reported that the N mineralized was correlated
with the N concentration, and was curvilinear to the C:N ratio. Specifically, the
relationship between percentage N mineralized and the C:N ratio of incorporated plant
residues best fit the equation: Y = bXm where b represents the intercept and m the slope.
They note this expression shows an inverse curvilinear relationship between the
percentage of N mineralized and increasing C:N ratio of the residues with a highly
5
significant correlation of r = 0.88. Palm and Sanchez (1991), Oglesby and Fownes
(1992), and Tian et al. (1992) used the polyphenolic concentrations in residues to predict
mineralized N, whereas Müller et al. (1988), and Kirchmann and Birgqvist (1989)
demonstrated that the lignin concentration of the residue was a useful predictor of N
mineralization rates. Vigil and Kissel (1991) combined six experiments from the
literature with two conducted by the authors to determine general relationships between
net N mineralized and the chemical characteristics of the residue. They predicted N
mineralized based on the C:N ratio, N concentration, and lignin concentration in the
residues. At 50% and 100% field capacity moisture regimes, Das et al. (1993) predicted
N mineralization rates on the C:N ratio and N concentration. Fox et al. (1990),
Constantinides and Fownes (1994), and De Neve’ and Hofman (1996) evaluated
combinations of these factors in predicting N mineralization from residues. Fox et al.
found a significant correlation (r2 = 0.866) between incorporated legume (lignin +
polyphenol):N ratio and N mineralization. Using incorporated vegetable crop residues,
De Neve and Hofman reported the amount of mineralized organic N was better correlated
to the C:N ratio of residue lignin, than the amount of total N, with 78% of the total
variance of mineralized organic N explained. Constantinides and Fownes, however,
concluded that differences among previous studies, in which chemical predictors were
best, arose from relatively small ranges in chemical composition of materials used. In
materials representing a wide range of chemical composition, initial soluble polyphenols
were secondary to initial N concentration in the residue in predicting total N mineralized.
Because of the increasing need to utilize animal manures and composts more
efficiently, many researchers have studied the properties that affect C and N
6
mineralization in these amendments. Soil texture appears to play an important role in
affecting mineralization rates. Castellanos and Pratt (1981) incubated several animal
manures in a San Emigdio fine sand and Holtville silty clay, and reported more N
mineralized in the fine sand for all types of manures. After incubating three broiler litters
and two turkey litters on one loam and two loamy sand soils, Westerman et al. (1988)
noted that more N was mineralized from the loamy sand soils for all litters. Sørensen and
Jensen (1995) found increasing net N immobilization with increasing clay concentrations,
and in a related study using N from sheep urine, found more N immobilization in a sandy
loam compared to a sandy soil. Gordillo and Cabrera (1997) found the lowest net N
mineralized in the soils of highest silt and clay concentrations, and highest N mineralized
in soils with the second highest sand concentrations, after incubating nine soils of various
textures with broiler litter. Egelkraut et al. (2000) reported that soils with higher clay
concentrations had longer time periods of initial N immobilization and mineralized less N
from added residues than those with lower clay concentrations. Ladd et al. (1981),
Sorensen (1983a,b), Merkx et al. (1985), Ladd and Amato (1988), and Voroney et al.
(1989) also reported on the stabilizing effect of clay particles. The increased stability of
soil organic matter in the presence of higher clay concentrations is due to its adsorption to
charged surfaces (Greenland, 1965; Oades, 1988) and physical protection from microbial
attack within small pores of microaggregates, which are more abundant in finer textured
soils (Adu and Oades, 1978; Young and Spycher, 1979; Elliot, 1986; Gregorich et al.,
1989). Zagal (1992) noted that microbial biomass concentration is related to soil texture
and presumed it was because higher clay concentrations increased the ability of soils to
preserve microbial biomass. However, Strong et al. (1999) stated that the protective
7
mechanisms of clay are undermined when a soil is dried and rewetted. They believe this
may be due to the clay limiting the diffusion of partially decomposed organic materials
away from the microbial decomposer population, facilitating more complete
decomposition of the organic matter.
Nitrogen mineralized from soil organic matter depends to a certain degree on soil
aggregate and particle size. Edwards and Bremner (1967) and Craswell et al.(1970)
suggest that soil organic matter may become inaccessible to microbial attack as soil
microaggregates are formed. Beare et al. (1994) indicated that macroaggregates in no-till
soil are an important mechanism for the protection of SOM that would otherwise
mineralize under conventional-till practices. Waring and Bremner (1964) noted
increased N mineralization rates with decreasing soil mesh size. Craswell and Waring
(1972a,b) ground soils to reduce aggregate size and observed higher N mineralization
rates. Hiura et al. (1976) suggested using the clay/humus ratio as an index of potentially
available organic N to microorganisms. Cabrera and Kissel (1988b) proposed the
clay/total N ratio of a soil to estimate the degree of protection clays provide organic
matter against microbial attack. Chichester (1969), McKeague (1971), and Cameron and
Posner (1979), conducted experiments that separated soils by particle size, and reported
decreasing particle size correlated with lower C:N ratios of soil organic matter, and that
the N mineralized as a percent of the total N of that fraction increased with decreasing
particle size. Cameron and Posner concluded this was primarily due to the fact that most
of the readily mineralizable N resided in mineral fractions of less than 4 µm, and much of
this was recently formed microbial tissues or metabolites.
8
Effect of moisture on C and N mineralization
The effect soil water content/potential on C and N mineralization from soil and
decomposing plant residues has been studied for some time. Greaves and Carter (1920)
noted that soils differing in relative saturation produced dramatically different levels of
nitrate after 21 days of incubation. Russell et al. (1925) found insignificant levels of
NO3-N in soils that were at the “hygroscopic coefficient”, but increasing amounts at the
highest level of moisture they studied, which was 1.25 times the “moisture equivalent” or
field capacity. More recently, Quemada and Cabrera (1997) showed that as soil matric
potential (ψ) increased from –5.0 to –0.003 MPa the total CO2 evolved from unamended
soil increased linearly with ln (-ψ), but CO2 evolved from decomposing clover residue
increased exponentially with ψ. By contrast, using undisturbed soils in laboratory
incubations, Sierra (1997) found that the rate of N mineralization showed a high degree
of variability, with 57% of the variation associated with factors other than moisture and
temperature. In field studies that confirmed the importance of moisture studies
conducted in the laboratory, Powers (1990) showed that soil temperature and moisture
strongly controlled the amount of N mineralized.
In a 30-week aerobic incubation study (Stanford and Hanway, 1955; Legg et
al.,1971), Stanford and Smith (1972) proposed the N mineralization potential (No) can be
estimated from the equation: log (No-Nt) = log No-k·t/2.303 or rearranged: Nt = No(1-e-kt)
where Nt is cumulative N mineralized at time t, No is mineralized N at time zero, t is
incubation time and k is the mineralization rate constant. Developing this work further,
Stanford et al. (1973) determined the rate constant k had a Q10 of approximately 2 within
the temperature range of 5-35o C. Maximum rates of N mineralization were reported by
9
Stanford and Epstein (1974) with soil moisture potential between –10 to –33 kPa for nine
different soils, then proposed a method to model the influence of soil water concentration
on N mineralization. The model normalized the various optimum water concentrations
of the soils, verified that the regression coefficients of N mineralized on soil water
concentration for the nine soils did not differ significantly (99% probability), then
derived the equation: Y = -3.9+ 1.02X (r2=0.93), where Y denotes relative N mineralized
and X denotes relative soil water concentration. Myers et al. (1982) modified Stanford
and Smith’s equation to express net nitrogen mineralized as a proportion of the maximum
rate versus a normalized moisture concentration fitted between –0.03 and –4.0 MPa.
Pilbeam et al. (1993) pretreated soils at different moisture concentrations for 24 days.
They measured, over a period of nine days, increased rates of N mineralization in soils
pretreated at higher moisture levels than lower moisture levels.
Cook and Allan (1992a) studied dissolved organic carbon (DOC) over 210 days in
soils maintained at a constant moisture, and found asymptotic exponential response
curves described positive associations between DOC and CO2-C mineralization rates at
early (14 and 35d) incubation times, but not later. The results reflected decreased DOC
utilization relative to supply, and suggested this could be caused by the accumulation of
recalcitrant DOC. In a related paper (Cook and Allan, 1992b) they determined, using the
Leenheer DOC fractionation scheme, that although they could not directly determine
DOC utilization, their results demonstrated that soil DOC was altered during the
decomposition of soil organic matter.
10
Effect of wetting and drying on C and N mineralization
Physically drying, then rewetting a soil may increase the rate of C and N
mineralization. Birch (1958) conducted several experiments in which he demonstrated
that when a soil was dried and rewetted, a flux of mineral carbon and nitrogen was
observed immediately after wetting. In earlier work Birch and Friend (1956) concluded
that successive wetting and drying released small amounts of decomposable material
from within the clay lattice where it had been protected from microbial attack. This view
was further developed to include the idea that a flush of decomposition was also due to
the high activity of the newly developing microbial population and the amount of
decomposable organic material that goes into solution (Birch 1959). Birch also provided
evidence to show that the amount of C mineralized was proportional to the C
concentration of the soil (Birch, 1960). Soulides and Allison (1961) found that prolonged
drying increased the rate of decomposition of the soil organic matter, and that multiple
drying events had a cumulative effect. A larger proportion of the bacteria died after the
first and second drying than after the third and fourth, inferring that younger cells were
killed more easily than older ones that were in a resting or sporulated stage. Stevenson
(1956), and Hayashi and Harada (1969) also reported the drying process resulted in the
killing of microorganisms. Marumoto et al. (1977a,b) concluded that dead microbial
cells and their cell walls were a major source of the decomposable soil organic matter.
Research conducted subsequent to Birch’s work in the late 1950’s confirmed that
periodic wetting and drying is correlated to higher CO2 production (Jager and Bruins,
1975; Herlihy, 1979).
11
Periodic drying and rewetting does not produce increased C and N mineralization
over soils kept continuously moist in all cases. Van Schreven (1967) noted that
intermittent drying at 35o C initially produced larger amounts of CO2, but less overall
compared to treatments kept continuously moist, when calculated over the entire 12-week
length of the experiment. He also indicated that the increase in the number of
microorganisms persisted days and weeks longer than the increase in CO2 production,
inferring that the younger bacterial population was the most active. Franzluebbers et al.
(1994) and Curtin et al. (1998) reported decreased C and N mineralization rates for soils
subjected to repeated wetting and drying compared to soils kept continuously moist.
White et al. (1998) reported decreased biodegradability, extractability, and uptake of
organic compounds such as phenanthrene and DEHP by earthworms in soils subjected to
repeated wetting and drying compared to soils kept constantly moist. However, based on
field and microcosm studies, Lundquist et al. (1999b) stated that the increase in dissolved
organic carbon (DOC) in soils exposed to wet-dry cycles indicates that wet-dry cycles
contribute to higher DOC concentrations in the soil solution. Baldwin and Mitchell
(2000) make the point that the extent of drying may determine whether more or less N is
mineralized. Partial drying of wet sediments may reduce N availability by producing a
zone for nitrification coupled with denitrification, while complete desiccation of the soil
may lead to the death of bacteria and subsequent mineralization of N.
Cabrera (1993) successfully modeled the flush of N mineralization that follows
rewetting, fitting the release to a modified Stanford and Smith (1972) equation, e.g.
Nt = No (1-e-k1
t) + kot, where k1 and ko are mineralization rate constants, and No, Nt, and t
are potential mineralizable N, cumulative N mineralized at time t, and incubation time,
12
respectively. He suggested the first-order N flush was superimposed on zero-order
background mineralization. In experiments utilizing 14C, Van Gestel et al. (1993b) fit
first order decay rates to biomass 14C and nonbiomass 14C. They concluded that soil
drying and rewetting promoted the turnover of C derived from added plant material, and
that this increase in C cycling was mainly due to enhanced turnover of microbial
products.
The effort to determine the proportional contributions of soil organic matter and
recently added plant residues to C and N mineralization has yielded unclear results.
Sørensen (1974) measured the CO2 release from 14C labelled glucose, cellulose, and
straw added to soil that was allowed to metabolize for a period ranging from 1.5 to 8
years. Air-drying and rewetting every 30 days over incubation periods of 260 and 500
days produced CO2 levels 16 to 121% higher than controls maintained at a constant
moisture level. Some of the difficulty in partitioning soil organic matter-C and plant
residue-C can be ascribed to the “priming effect” reviewed by Jenkinson (1966a). The
priming effect states that the addition of plant residue to a soil can increase the
mineralization rate of soil organic matter as compared to controls without addition of
plant residue (Sørensen, 1974).
Carbon and nitrogen mineralization rates based on microbial
biomass response to repeated wetting and drying
Seneviratne and Wild (1985) attributed the effect of drying on nitrogen
mineralization to two causes: the death and subsequent lysis of a small proportion of the
soil organisms, and desorption of organic substances with a wide C/N ratio. Van Gestel
13
et al. (1993a) inferred that the sources of mineralization flushes were partly biomass
killed by drying, and partly non-microbial organic residues, and that the size of the
flushes seemed to be influenced by soil properties such as C concentration and soil
texture.
Kieft et al. (1987) demonstrated that most microbial biomass lysis occured at
rewetting, not during the slow drying period, explaining that slow drying allows microbes
to adjust osmotic potential to their surrounding environment, but rapid rewetting causes
cell rupture. Cortez (1989) noted that not all soil biomass undergoes lysis during
rewetting, suggesting the presence of an active and a dormant fraction of soil biomass.
De Bruin et al. (1989) postulated that the only microbial growth taking place after 30
days in a rewetted soil was based on the turnover of C and N from the microbial biomass
itself. Bloem et al. (1992) utilized direct microscopy to note that while bacterial numbers
did not change significantly, O2 consumption and N mineralization decreased during a
drying period, yet respiration increased up to 1.5 fold and N mineralization increased up
to 5 fold following rewetting. This was attributed to the frequency of dividing-divided
cells (FDDC), which increased up to 23% over soils maintained at constant moisture.
Stark and Firestone (1995) demonstrated the relative importance of microbial cell
osmotic potential and substrate diffusion in a drying soil on microbial activity, finding
that substrate limitation was the major inhibiting factor when soil water potentials were
greater than -0.6 MPa, but adverse physiologic effects due to cell dehydration was more
significant in soils with water potentials less than –0.6 MPa. In a field study
investigating differences in conventional, low-input, and organic farming systems,
Lundquist et al. (1999b) suggested surface microbial populations had adapted to wet/dry
14
cycles over a three month growing season, leading to changes in microbial process rates
and community composition. Kuikman et al. (1991) pointed out that protozoa play a role
in N mineralization by reducing the number of bacteria and increasing the mineral N
concentration in the soil. In experiments that contrasted continuously moist soils with
those allowed to fluctuate, they showed that protozoa stimulated the mineralization of N
5-10% compared to soils without protozoa.
Compost and leaf litter in C and N mineralization
As crop residues decay, they form an important component of organic C and
organic N in the soil. Portions of these organic compounds are mineralized over time to
provide a source of energy to soil flora and fauna. Several studies have utilized crop
residues or composts to observe rates of C and N mineralization in soils.
Appel and Mengel (1993) reported decomposition and mineralization of sugar beet
leaves incorporated into soils enhanced available N for plants, reflected by an increase of
inorganic soil N, as well as of extractable organic N fractions. They concluded from their
study on sandy soils that the extractable soil organic N fractions reflect the soils’
microbial activities, and represent easily-mineralizable N pools in sandy soils.
Franzleubbers et al. (1995) reported soils with microbial biomass ranging from <10 to
1042-mg C kg-1; soil organic C ranged from 2.0 to 13.7-mg kg-1. Cowpea leaves
incorporated into the soil had 458-g C kg-1, and a N concentration of 36-g kg-1, for a C:N
ratio of 12.7. While initial C and N mineralization rates in a subsoil were less than topsoil
treatments, at the end of 60 days total C and N mineralization were not significantly
different, indicating microbial biomass adjusted quickly to the new substrate, regardless
15
of preexisting conditions. In a study of cotton grown on non-irrigated Ultisols, Mullins
and Burmester (1990) found cotton leaf dry matter production to range between 942 and
1466 kg ha-1.
Airan and Bell (1980) define composting as a process for decomposition of organic
solid wastes into relatively stable humus-like materials, and that the decomposition
process is accomplished by various microorganisms including bacteria, actinomycetes,
and fungi. He et al. (1992) note that when discussing municipal solid wastes (MSW)
various operational parameters, such as source and nature of the raw material, source
separation, composting temperature, moisture content, degree of aeration, and
composting duration can significantly affect compost properties. While acknowledging
the difficulty in making a general description of all MSW composts, they note that the
moisture content of most composts varies between 20 and 50%, ash content is about 50%,
C content is 30% on a dry-weight basis, and pH is generally neutral or slightly higher.
De Haan (1981) found that while MSW compost is higher in N and P than most
agricultural soils, only 10 to15% of the total N is available the first year, and no residual
effect remains in the second year. Navarro et al. (1992) applied 2.7 and 9.0-g MSW
compost per 100-g soil, calculated according to the N needs of rye grass, assuming 50%
N mineralization in the lower rate. “Mature compost” (not defined) contained 27.1% C,
1.5% N, and a C:N ratio of 18.1. Total organic N in the soil (soil not classified) ranged
from 0.11 to 0.31-g N per 100-g soil. They found initial N immobilization, lasting three
to five weeks, in a study conducted at field capacity and constant temperature (28o C).
Sikora and Yakovchenko (1996) used a MSW compost that contained 146-g C kg-1, 12-g
N kg-1, and a C:N ratio of 12.3, to study soil organic matter decomposition after
16
amending with compost. They conclude that if a priming factor exists, as discussed
earlier, it is of low magnitude, short duration, and would not be a significant benefit in
providing mineral N to plants. Their data suggests that the beneficial effects of adding
composts to soil are not due to increased mineralization of SOM C or N within the first
1440 hours. The benefits of adding compost to a soil may be more related to improved
soil physical properties, such as reduced compaction and higher water holding capacity.
Mamo et al. (1999) utilized two different composts over three years with organic carbon
ranging from 17 to 24%, N from 0.9 to 1.1%, and C:N ratios from 15 to 27. They applied
this material at rates equivalent to 90 to 270 Mg ha-1. At the end of the 64-day incubation
period the composts mineralized less than 0.2% of the total soil N, while N mineralized
in the control soil was 1.6% of the total soil N. Egelkraut et al. (2000) used a MSW
compost and cotton leaves and stems as incubation materials in a study comparing C and
N mineralization in soils differing in texture. The compost contained 36.74% C, 12.74%
organic N, and a C:N ratio of 28.8. The cotton leaves were 43.84% C, 28.3% organic N,
and had a 15.5 C:N ratio. The compost had net N immobilization for the first 47 to 131
days of the study, depending on soil type. While cotton leaves initially immobilized N,
all soil types had net mineral N accumulations after 7 days, with increasing N
mineralization until the 179 day end of the study.
In contrast to MSW composts, composted dairy manures released 11 to 29% of their
total N content as inorganic N after 32 weeks. Composted manure contained, on average,
33.2% organic matter and 2.4% N (Hadas and Portnoy, 1994). They noted that while no
immobilization occurred, N mineralization rates were suppressed compared to the
controls during the first week. They postulate that this is due to N assimilation by
17
microbes, as evidenced by high initial CO2 rates. In a field study on the effect of
applying MSW compost (C:N ratio 40:1) at different rates, Eriksen et al. (1999) observed
that soil NO3-N was inversely proportional to MSW compost rates the first year. In the
second year, though, there was an increasing supply of plant-available N, due to
mineralization of organic N in the MSW compost with increasing MSW compost rate;
however, the supply of mineralized N was inadequate to meet crop growth requirements
for maximum maize (Zea mays) yield.
18
CHAPTER 1
PRELIMINARY WORK TO STUDY THE EFFECT OF DRYING ON C AND N
MINERALIZATION
Introduction
In order to quantify the effects of drying on C and N mineralization, an experimental
system was needed that would either allow relatively rapid drying of soil or maintain soil
moisture, while in both cases providing sufficient oxygen to maintain normal respiration
rates. Preliminary studies were conducted to ascertain whether an aquarium system would
fulfill the requirements of the experiment, and to ensure mineralized C and N were
collected accurately without interfering with, or causing damage to, the system. These
studies included placing pre-moistened soil treatments in the aquarium to determine
moisture retention over time; quantifying the volume of leachate needed to extract
mineralized N on a periodic basis; observing CO2 evolution from treatments in order to
determine best sampling times; and gathering rainfall data from the Georgia Coastal Plain
to determine the length of the drying period for the soil treatments.
Materials and Methods
Our objective was to study the effect of wetting and drying on N mineralization.
Preliminary studies were carried out to determine the time required to dry soil from field
capacity to air-dry. Treatments were separated into two (25.5 x 51 x 30.5-cm) aquariums,
19
with one aquarium maintained at a constant, moisture-saturated humidity, and the other
maintained at the humidity of the laboratory air. Each aquarium was covered in black
duct tape to prevent light penetration, in order to avoid algae growth. A 31-L aquarium
was selected for this purpose, modified with stainless steel lids, with 4-mm air-entry and
air-exit ports, covering the tanks. Air was pumped in by means of two Second Nature®
Challenger 1™ aquarium air pumps that forced 4-L air minute-1 through Nalgene®
(Nalge Nunc International Corporation, Rochester, NY) premium, Grade VI, (1/8” ID)
tubing, 60-cm long into either a carboy partially filled with 4-L deionized water, or a dry
glass bottle, depending on the treatment. For the wet treatment the air continued down a
tube until it bubbled into the deionized water in the bottom of the carboy. Moisture
saturated air then escaped at the top of the carboy through a 90-cm long, Nalgene®
premium, Grade VI, (1/8” ID) tube into the aquarium. The aquarium for the wet
treatment contained a 2-cm layer of deionized water in the bottom of the tank, while the
aquarium for the dry treatment did not. For the dry treatment, air was pumped from the
dry glass bottle through a 90-cm tube into the aquarium. Each aquarium contained two
removable, porous, stainless steel shelves to hold the soil containers.
Experimental units consisted of 100-g oven-dry equivalent soil placed in a
Nalgene® 70-mm diameter, polypropylene Buchner funnel top (funnel portion
removed), after a Supor®-450 (Pall Gelman Sciences, Ann Arbor, MI) 0.45µm polymer
filter was placed in the bottom of the Buchner funnel top. Triplicate replications of all
treatments were brought to field capacity (-0.01 MPa) with deionized water and placed in
their respective aquariums, and weighed daily to the nearest 0.1g, on an O’Haus Model
No. AP210-0 scale (O’Haus Corporation, Florham Park, NJ), for eleven days. The soils
20
utilized were a Norfolk loamy sand, (coarse-loamy, kaolinitic, thermic Typic
Kandiudults), and an Orangeburg sandy loam (fine-loamy, kaolinitic, thermic Typic
Kandiudults), that were air-dried, crushed, and passed through a 2-mm sieve to remove
small rocks and crop residues (< 1% of soil weight).
Soil treatments were brought to field capacity by placing 100-g oven-dry equivalent
soil in the Buchner funnel attached to a vacuum source, first covering the floor of the
funnel with a 0.45-µm polymer filter paper. The soil was smoothed and gently tamped
down with the bottom of a volumetric flask. A Whatman #42 filter paper was custom cut
to completely cover the soil in the flask and placed on top of the soil. 60.0-mL deionized
water – representing 15% moisture, which exceeds the known field capacity of these soils
- was poured slowly over the top filter, taking care to thoroughly and evenly wet the
filter. The deionized water was allowed to drain gravimetrically for 30 min. Vacuum
was applied for 30 min and allowed to run until all excess moisture had drained. The
funnel weights were weighed and recorded (Figure 1.1).
To determine an appropriate volume of leaching solution to remove NO3-N from
100 g of residue treated soil in buchner funnels, a preliminary experiment was conducted
using Cl- ions as a substitute for NO3-N, since Cl- has been shown to move similarly to
NO3- in soils (Nielsen and Biggar, 1961). Background soil Cl- levels were determined by
combining 100.00 g soil with 400 mL H20 in a 600-mL beaker and titrating with 0.0065
M Ag2SO4. Three separate KCl solutions were formulated so that each soil could be
brought to its field capacity with a KCl solution that would have 12.66 mg Cl- kg-1 soil.
These solutions were pipetted into the appropriate soil to bring them to field capacity.
They were allowed to equilibrate overnight in the moist-air aquarium, then were leached
21
with 50-mL aliquots of deionized H2O under vacuum. The 50-mL aliquots were titrated
with 0.0065 M Ag2SO4 to an endpoint of 290-mv with a Beckman 39048 silver
electrode/calomel electrode (Beckman Instruments, Inc., Fullerton, California) in order to
calculate percent chloride recovery (Figure 1.2). The reaction is:
Ag2SO4 + 2Cl- -> 2AgCl(s) + SO42- [1.1]
One objective of the main experiment was to evaluate the rate of CO2-C mineralized
from the treatments. To determine the appropriate measurement times, a preliminary
experiment was conducted to measure the rate of CO2 loss from three soils with two
organic residues using an infrared gas analyzer (IRGA). Soils used were the Orangeburg,
Norfolk, and Norfolk depressional, described earlier. 100.000 g of each soil were mixed
thoroughly with either 0.2057 g ball-milled cotton leaves or 1.5005 g ball-milled
compost, and placed in a 70-mm diameter Buchner funnel top with a 0.45 µm polymer
filter. Soil in the funnels was brought to field capacity (-0.01 MPa) by pipetting
appropriate quantities of deionized water. The base of the funnel was sealed with Saran®
wrap. Lids made of Poly-vinyl Chloride that were machined for a rubber O-ring sealed
the top. A rubber septum was placed in the middle of the PVC lid to allow air to be
pumped through by syringe injection. Air was pumped using aquarium air pumps
described earlier into a glass bottle containing M NaOH to scrub the CO2 out of the air.
22
The reactions are:
H2O + CO2 → H2CO3 [1.2]
H2CO3 + 2NaOH → Na2CO3 + 2H2O [1.3]
The CO2-scrubbed air passed into the sealed treatment container head space. Air
then passed into a Li-Cor IRGA CO2 Analyzer, Model LI-6252 (Li-Cor, Inc., Lincoln,
NE) which measures µmol CO2 mol-air-1. Using a flow meter µg CO2-C g-soil-1 hr-1
were calculated according to the following equation:
(Flow rate (mL min-1) x 0.06) / 22.4 x IRGA reading (µmol CO2 mol air-1) x 12 / g soil
[1.4]
where flow rate x 0.06 = liters of air hr-1; L hr-1/22.4 = mol air hr-1 (22.4-L is volume of
one mol air at standard temperature and pressure) The volume of air in liters was
corrected for temperature and pressure as recorded during the experiment according to
the formula given in the handbook of Chemistry and Physics, 45th edition, 1964,1965,
which is:
density of dry air (g mL-1) = (0.001293 / (1+ 0.00367t)) x (H/76) [1.5]
where t is temperature in degrees C, and H is pressure in cm mercury. The density of dry
air was multiplied by 1000 to obtain g L-1. The formula weight of air, for the major
23
components N, O, CO2, and Ar, as calculated from the Handbook of Chemistry and
Physics, 45th ed, is 28.953, so 28.593 g / the density of dry air (g L-1) gave L.
Readings were taken approximately every hour for the first 24 hours, with time between
readings expanding as the project progressed.
Precipitation data was gathered from three research locations located in the Coastal
Plain of Georgia. Data from the National Peanut Research Laboratory, U.S.D.A – A.R.S.
near Dawson, The Coastal Plain Experiment Station, University of Georgia, near Tifton,
and the Catahoula Farm, University of Georgia, near Cordele, was analyzed to determine
the frequency of rain events, and the number of days between rain events, over a
“growing season”. The growing season spanned March 15th to October 15th, to roughly
coincide with average planting and harvesting dates for the area, with data covering the
years 1997 through 2001. Rain events equaling or exceeding 0.25-cm day-1 were
enumerated, then totaled. The 215-day span covered was divided by the number of rain
events for that season to obtain an average number of days between rains. For all
locations covering all years the average number of days between rain events was 6.00
days with a standard deviation of 1.49.
Because rain events often clustered, a second method was used to evaluate days
between rain events. The rationale was to calculate the mean number of consecutive days
with no rain, so that it could be determined how many drying days the soil had on
average. Days that contained less than 0.25-cm precipitation were counted as “dry” days.
Using this method, the average number of consecutive days between rain events was
6.89. There was quite a bit of variability in the number of days between rains, for a given
location over a given growing season, as the average standard deviation was 6.81. The
24
longest time span between rain events equaling or exceeding 0.25-cm was 70 days,
occurring between July 2 and September 9th, 1997 at the Catahoula Farm near Cordele.
The average number of days between rain events was close to seven. The
preliminary tests to dry the soil treatments revealed that it took at least eight days in the
laboratory to reach air-dry. Therefore, it was decided for the main experiment to allow
eight days to dry the soil to air-dry, then an additional three days to place the soil biota
under stress, before rewetting.
Results and Discussion
At field capacity (-0.01MPa) the Orangeburg soil held 0.103 g H2O per gram of soil,
while the Norfolk held 0.080 g H2O per gram of soil. Over the study, treatments
maintained in the moist environment (~98% RH) lost 0.00577 g H2O g-1 Orangeburg soil
or 0.58% of the total moisture, and 0.00398 g H2O g-1 Norfolk soil or 4.98%. Treatments
maintained in the laboratory-dry air (~50% RH) evaporated 0.0975 g H2O g-1 Orangeburg
soil or 94.66%, and 0.0771 g H2O g-1 Norfolk soil or 96.38% (Figure 1.1). Most
evaporation occurred the first eight days of the test, however it was presumed it would
take longer to dry the treatments during the actual experiments due to an increased
volume of treatment replications in the confined space of the aquariums. This
preliminary test showed the forced-air aquariums were sufficient in maintaining adequate
moisture in the moist-air tank, and sufficient in allowing soils at field capacity to
evaporate moisture to air dryness (-100MPa).
In all soils and all replications, over 90% of the Cl- ions were recovered after 200
mL of deionized water were used to leach the treatments (Figure 1.2). The Norfolk soil
25
recovered 90.5% of chloride ions after four 50-ml aliquots of leachate, and 92.4% by five
50-mL aliquots. The Norfolk depressional recovered 93% of chloride by four 50-mL
aliquots, and 94.1% by five 50-mL aliquots. The Orangeburg soil recovered 97.9% by
four 50-mL aliquots, and 98.9% by five 50-mL aliquots. After 400-mL of leachate were
extracted, the Orangeburg recovered 102.1% of chloride. A possible explanation for this
is that the Orangeburg soil sample used, had more chloride in it than calculated from the
soil extraction portion of the experiment. Based on these results, it was decided 250-mL
leachate would be used in the main experiment in order to provide a margin of safety.
After integrating for total CO2-C mineralized, soils with cotton leaves mineralized
an average of 109% more CO2-C than soils with compost residue. The Norfolk
Depressional with cotton leaves evolved the most CO2-C at 0.257 mg CO2-C g soil-1.
The least amount of C mineralized as CO2 occurred in the Norfolk soil with compost at
0.069-mg CO2-C g soil-1. The study lasted 160 hr, with the majority of C released in the
first 48 hr. The Orangeburg soil, with the greatest clay content of the three soils, but less
soil organic matter than the Norfolk depressional, evolved 0.225 mg CO2-C g soil-1 with
cotton leaves, and 0.119 mg CO2-C g soil-1 with compost. The soil with moderately high
clay and highest organic matter of the three soils, released the most CO2-C, while the
sandiest soil with the least soil organic matter released the least CO2-C (Figure 1.3).
From this preliminary study of CO2-C mineralization, the decision was made to sample
for CO2 every 24 hours for two days after leaching, which rewet the soil, then at least
every 48 hours until the next leaching event.
26
Time (days)0 2 4 6 8 10 12
g H
2O g
-1 so
il
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
0.12
Orangeburg, constant moistureNorfolk, constant moistureOrangeburg, air dried Norfolk, air driedzero
Figure 1.1 Loss of water content in Orangeburg and Norfolk soils in chambers maintained at 98 % and 50% RH.
27
Figure 1.2 Cumulative % Cl- recovery from coastal plain soils in 50 mL aliquots.
Deionized water (ml)100 200 300 400
Cum
ulat
ive
% C
l- reco
very
40
50
60
70
80
90
100
110
NorfolkOrangeburg Norfolk depressional
28
IRGA CO2-C - Orangeburg IRGA CO2-C - Norfolk depressional
Figure 1.3 CO2-C evolved from coastal plain soils over 165 hours, as measured by infra-IRGA CO2-C - Norfolk
Time (hours)
0 20 40 60 80 100 120 140 160 180
µ g C
O2-
C g
soil- 1
hr- 1
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
cotton leavescompost
Time (hours)
0 20 40 60 80 100 120 140 160 180
µg C
O2-
C g
soil-
1 hr
-1
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Time (hours)
0 20 40 60 80 100 120 140 160 180
µg C
O2-
C g
soil-
1 hr
-1
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
red gas analyzer (IRGA), to determine initial rates of CO2-C evolution from soils with incorporated residues.
29
CHAPTER 2
THE EFFECT OF WETTING AND DRYING ON NITROGEN
MINERALIZATION
Introduction
Many factors influence the rate of N mineralization in soils, including temperature,
moisture, soil texture, soil organic matter, and crop residue composition. Some studies
have focused on the effect moisture has on rates of N mineralization from soil organic
matter (Stanford and Smith 1972, Stanford and Epstein 1974, Sierra 1997), while others
have studied the effect moisture has on N mineralization from residues (Curtin et al.
1998, Das et al. 1993). Birch (1960) studied the effect wetting and drying had on N
mineralization, with dry periods ranging from 3 to 15 weeks. Cabrera (1993) modeled
the initial flush of N mineralization occurring hours after rewetting a dried soil.
The purpose of this study was to determine the effect repeated wetting and drying
would have on the rate of N mineralization on coastal plain soils of the southeastern
United States with different residues incorporated. The study was conducted over 185 d
to simulate the approximate length of the growing season for a summer annual crop.
Materials and Methods
Three soil samples were collected from the upper 0.15 m of a field under
conventional tillage in the coastal plain of Georgia to provide a range of clay and soil
30
organic matter contents. The Norfolk loamy sand (coarse-loamy, kaolinitic, thermic
Typic Kandiudults) contained both the lowest clay percentage and the lowest soil organic
matter. The Orangeburg sandy loam (fine-loamy, kaolinitic, thermic Typic Kandiudults)
contained the highest clay content and the medium level of soil organic matter of the
selected soils. The Norfolk depressional sandy loam (fine-loamy, kaolinitic, thermic
Arenic Kandiudults), a taxadjunct to the Norfolk series, contained a medium clay level
and the highest soil organic matter content of the three soils (Table 2.1). Soils were air
dried in the laboratory, crushed, then sieved through a 2-mm sieve to remove small rocks
and non-decayed crop residue, which constituted less than 1% of the soil by weight. The
water content of the soils at field capacity (–0.01 MPa) was determined by using a
pressure chamber. Three replicates of each soil were placed into steel cores with a 2-cm
radius and 0.9-cm height and saturated with deionized water at atmospheric pressure. The
samples were placed into the pressure chamber (Soil Moisture Equipment Co., Santa
Barbara, CA) and brought to –0.01 MPa, weighed, dried in an oven at 105 o C for 48
hours, then weighed again (Klute, 1986). A subsample of each soil was analyzed for C
and N with a Carlo-Erba NA 1500 Analyzer for Carbon and Nitrogen, Milan, Italy,
according to the methods described by Kirsten (1983).
The study treatment design was a factorial combination of three soils (Norfolk,
Orangeburg, Norfolk depressional), three residues (none, cotton leaves, compost) and two
soil water levels (constant wet and alternating wet and dry). Organic residues chosen for
the study were cotton leaves and compost. The compost selected began as a mixture of
grass clippings, hardwood leaves, and pine needles. Windrows were stacked 120 cm high
and mixed until the materials went through a peak heat. Samples were sieved in a 2-mm
31
sieve, composited, and ball milled. A subsample was analyzed for C and N (Table 2.2)
with a Carlo-Erba NA 1500 Analyzer for Carbon and Nitrogen. Cotton leaves were
applied at 2057 mg kg-1 soil, and compost was applied at 15000-mg kg-1 soil. After
placement of a 0.45-µm Supor® 450 membrane filter (Gelman Sciences, Ann Arbor, MI)
filter in the bottom of a (75-mm diameter x 40 mm height) buchner funnel, residues were
mixed with soils by placing the weighed soil and residue into the buchner funnel, then
stirring with a glass rod for 5 min. Soil that fell through the bottom of the buchner funnel
was captured by placing the funnel on paper during stirring, then pouring the soil back
into the buchner funnel. There were three replicates of all treatments.
Treatments were divided into two systems. Those maintained at field capacity for
the duration of the study were kept in an aquarium (25.5 x 50 x 30.5 cm) whose external
surface was taped with black duct tape to prevent algae growth. The bottom 2 cm of the
tank held deionized water to help maintain high humidity. The top of the tank was
covered by a stainless steel lid with 4-mm (inner diameter) entry and exit ports. Air was
pumped in by means of two Second Nature® Challenger 1™ aquarium air pumps
providing 4L min-1 air through Tygon® tubing into the bottom of a carboy partially filled
with 4L deionized water. Water-saturated air then exited through the top of the carboy
via Tygon tubing into the entry port for the tank. Treatments that were dried and
rewetted were stored in the high humidity tank for 3 d, then transferred to an identical
tank that had laboratory air pumped into a dry glass bottle, then transferred into the entry
port of the stainless steel lid. The bottom of the dry tank contained no water, but instead
held 454 g Drierite® (W.A. Hammond Drierite Co., Xenia, OH) anhydrous calcium
sulfate, that was changed daily. Soils were dried down in this tank for 11 d before being
32
rewetted. Temperature and relative humidity levels inside the tanks were recorded for
both treatments two times per week.
Following the first 14-d cycle, all soils were weighed and the Buchner funnel tops
containing the soil was attached to their funnel bottoms and inserted into a vacuum flask
in preparation for leaching. A Whatman #42 filter paper disk was placed on top of the
soil and 100 ml of 0.01M CaCl2 was added, taking care to not disturb the soil, and
allowing it to drain by gravity only. Then vacuum was applied, and more CaCl2 was
added in 50-mL aliquots, until a total of 200 mL was applied. This was followed by 50
mL of a N-free nutrient solution containing 430.48 mg L-1 CaSO4, 243.41 mg L-1 MgSO4,
2.19 mg L-1 KH2PO4, and 15.02 mg L-1 K2SO4. The leachate was stirred, transferred
quantitatively, and brought to volume with 0.01M CaCl2. The samples were stored in a
freezer at -20o C, until analyzed. After removal of the Whatman #42 filter paper disk, soil
residue was scraped from the disk back into the treatment container. The 14-d incubation
cycle was repeated a total of 13 times over 185 days. At the end of 185 days, all
treatments were air-dried and weighed, then oven-dried and reweighed.
Nitrate was analyzed on a Dionex DX-120 IC (Sunnyvale, CA), which determined
concentration based on electrical conductivity. Standards were made up in 0.01M CaCl2.
Ammonium was analyzed on an OI Analytical Flow Solution 3000 (College Station, TX)
using the automated phenate colorimetric procedure EPA-600/4-79-020, “Nitrogen,
Ammonia” Method 350.1 (EPA, March 1984). Statistical analysis (GLM procedure) of
the net N mineralized after 185 d of incubation was conducted using SAS (SAS Institute,
1985), followed by testing for mean separation, using Tukey’s method.
33
Soluble organic C analysis was conducted by injecting 3 mL of the 0.01M CaCl2
leachate through a 0.45 µm filter, then analyzed on a Shimadzu TOC-5050 (Shimadzu
Corp., Kyoto) total organic C analyzer. The TOC-5050 combusts the sample and C is
converted to CO2, which is then quantified by a non-dispersive infrared gas analyzer
(NDIR), where CO2 is detected. The NDIR outputs an analog signal, which generates a
peak whose area is calculated by a data processor.
Results and Discussion
In the control soils with no residue, the greatest amount of N mineralized came from
the Norfolk depressional (Table 2.3). The Orangeburg and Norfolk mineralized
statistically the same amount of N at α = 0.05. By the end of the study, the control soils
all mineralized between 4-8% of organic N present at the beginning of the study. The
Orangeburg soil slightly immobilized N in the first 14 d; the Norfolk soil mineralized
18.8% of its total N mineralized, in the first 14 d; and the Norfolk depressional
mineralized 39.1% of its total N mineralized, in the first 14 d (Figure 2.1). There was a
steady increase in the cumulative N mineralized over time for all soils after 14 d (Figure
2.1). For control soils, the moisture regime did not significantly affect the rate of N
mineralized at the α = 0.05 level for the soils (Table 2.3). The soil type was a significant
factor at the α = 0.05 level, confirming previous work by Egelkraut et al. (2000).
Tukey’s method of mean separation revealed that the Norfolk depressional was different
than the Norfolk and Orangeburg. A soil x moisture interaction was considered and
analyzed with the GLM procedure, and it showed no significant interaction at the
34
α = 0.05 level. Residual analysis was performed and showed the samples to be normally
distributed, verifying the model.
Cumulative N mineralized, as % of N applied, for soils with incubation materials, is
shown in Figure 2.2 for each of the moisture regimes. The GLM procedure was used to
identify significant differences in % N mineralized from residues at the α = 0.05 level
(Figure 2.4). Moisture regime was a significant factor, as were soil type and residue.
Interactions were investigated and showed a significance for moisture x residue, but not
for soil x moisture, soil x residue, or soil x moisture x residue. After means testing, using
least square means, the moisture x residue interaction, it is apparent that when treatments
are under constant moisture there is a significant difference between residues, but when
treatments are repeatedly wetted and dried they are not significantly different (Figure
2.3). Residual analysis was performed and showed the sample data to be normally
distributed, verifying the model (not shown).
For all soils, the most N mineralized after 185 d, as % of N applied, was from cotton
leaves in the constant moisture regime. For all soils, cotton leaves displayed an initial
period of N immobilization, as indicated by the negative portion of the curves in Figure
2.2, but showed faster net N mineralization in soils under a constant moisture regime than
the soils that were subjected to repeated wetting and drying. The Orangeburg soil with
cotton leaf residue that underwent repeated wetting and drying had no net N
mineralization after 185 d.
At 185 d, for soils maintained at a constant moisture regime, the Orangeburg,
Norfolk, and Norfolk depressional with cotton leaves had 25.7, 28.5, and 39.5%
mineralized N as % applied, respectively. After 185 d, in soils with cotton leaves
35
undergoing repeated wetting and drying, the Norfolk soil had 2.0% mineralized N as % N
applied, the Norfolk depressional had 6.85%, while the Orangeburg had 1.28 %
immobilized N. There was a strong contrast in mineralization trends between soils with
cotton leaves under a constant moisture regime versus repeated wetting and drying.
While both sample populations initially immobilized N, those under constant moisture
regime mineralized N by 45 d. By 58 d, 38-68% of the total N mineralized, had
undergone mineralization. After 58 d, the rate of N mineralization appeared to slow
down, as the remaining cotton leaf residue apparently became more difficult to break
down, or microbial populations stabilized. Soils with cotton leaves subjected to repeated
wetting and drying initially immobilized N, then mineralized N only slowly. At the end
of 185 d, the Orangeburg still had net N immobilization, the Norfolk had 2% net N
mineralization, and the Norfolk depressional 6.9% net N mineralization. The Norfolk
had net N mineralization after 129 d, and the Norfolk depressional had net N
mineralization after 58 d.
The cause of the difference in net N mineralization is not yet understood for this
study. It is possible that the N not mineralized in the repeatedly wetted and dried
treatments is still in the soils. It may be possible to verify this with a follow-up study
incubating the treatments for 60 d under constant moisture conditions and then leach
them with 1 M KCl. If, in the follow-up incubation study, the treatments that were under
fluctuating moisture conditions in the initial study, mineralize significantly more N than
the treatments that were under constant moisture in the initial study, it may indicate the N
in the repeatedly wetted and dried soils did not mineralize much N in the initial study.
Another possibility was that some N denitrified during the rewetting procedure. If
36
organic C analysis of the leachates revealed higher total C in the wetted and dried
treatments than the constant moisture treatments, it may have been an indication that
denitrification occurred. The presence of higher amounts of soluble C in the leachate,
coupled with less mineral N in the leachate, could indicate the presence of denitrifiers,
since denitrifiers would contain soluble C, but would have evolved N as N2O gas
(Cabrera M.L., personal communication, 2002). An analysis of soluble organic C in the
0.01M CaCl2 leachate revealed, however, less C in the repeatedly wetted and dried soils
than those maintained at a constant moisture level (Figure 2.4).
Soils with compost either did not have any initial net N immobilization, or it was
slight (<2%) and only lasted 14 d. The amount of N mineralized by 185 d was relatively
small, regardless of moisture regime. Soils with compost maintained at a constant
moisture level mineralized 3.8 to 9.3% of the N applied as compost, and soils that
underwent repeated wetting and drying mineralized 1.6 to 3.3% of the N applied. There
was a significant difference in N mineralized (α=0.05) between moisture regimes for the
Orangeburg and Norfolk depressional soils, but not the Norfolk soil (Table 2.3). There
was no significant difference in the amount of N mineralized between soil types (α=0.05)
for soils treated with compost. The Orangeburg and Norfolk soils with compost
maintained under constant moisture did not immobilize N. The Norfolk depressional
with compost initially immobilized N, but had net N mineralization by 32 d, and
mineralized more N than the other two soils as %N applied. The Norfolk depressional
immobilized the most N of the soils with compost (1.9% of the compost N after 14 d).
The net amount of N mineralized from compost by 185 d was 9.3% for the Norfolk
depressional under constant moisture, 3.2% for the Norfolk depressional repeatedly
37
wetted and dried, 3.8% for the Norfolk under constant moisture, 1.7% for the Norfolk
repeatedly wetted and dried, 4.9% for the Orangeburg under constant moisture, and 1.6%
for the Orangeburg repeatedly wetted and dried (Table 2.3). These values are in line with
previous results obtained by Tyson and Cabrera (1993), that showed 0.4 – 5.8%
mineralized N in composted broiler litter.
It may be of interest to note that although there was a significant difference in the
amount of N mineralized between the cotton leaves and compost (Table 2.3), there was
not much difference between the C to N ratios of the two residues (Table 2.2). While the
Orangeburg soil mineralized, in almost all cases, the least amount of N from the residues,
it had the lowest C to N ratio of the three soils (Table 2.1). This may suggest that the C to
N ratio of the soil organic matter had an impact on the quantity of N mineralized from
residues. The higher C to N ratio of the Norfolk depressional soil, compared to the
orangeburg soil, may indicate a higher C to N ratio in the base microbial population in
the Norfolk depressional. A microbial population with a higher C to N ratio would
require less N and therefore mineralize more N from the applied residues.
For all soils and all residues there was a significant difference between treatments
maintained at constant moisture versus treatments subjected to repeated wetting and
drying at α=0.05. Soils maintained at constant moisture exhibited more N mineralized
than those wetted and dried. The mean N mineralized for all soils with compost under
constant moisture was 5.99%, while the mean N for all soils with compost repeatedly
wetted and dried was 2.18% (LSD = 2.71). The difference for all soils with cotton leaves
was more dramatic, with the mean N mineralized for all soils with cotton leaves under
constant moisture was 31.23%, while the mean N mineralized for all soils with cotton
38
leaves repeatedly wetted and dried was 2.54% (LSD = 9.56). The initial amount of
inorganic N in the compost was equivalent to 14.38 mg N kg-1 soil, and the initial amount
of inorganic N in the cotton leaves was equivalent to 1.17 mg N kg-1 soil.
In Stanford and Epsteins’ study of the relationship between soil water content and
nitrogen mineralization (Stanford and Epstein, 1974), they established that at 35o C, the
relative rate of N mineralization was equal to the soil water content / optimum soil water
content. For example, at 40% of optimum water content (optimum water content was
noted as 1/3 bar), one would observe 40% of the mineralization rate as at 100% optimum
water content. The average soil moisture for the soils repeatedly wetted and dried was
49.9% over the length of the study. Based on Stanford and Epstein’s work, one would
expect roughly half the N to mineralize compared to the soils maintained at field
capacity. For all control soils with no residue, there was no significant difference between
N mineralized under optimum water conditions and N mineralized under repeatedly wet
and dry conditions. This may suggest rewetting had a mechanistic or biological effect
that overcame periods of dry soil with low biological activity and ensuing low N
mineralization. Kieft et al. (1987) noted an increase in biomass-C release as inorganic C,
following rapid rewetting, and a greater proportion of biomass-C release after a 6.9MPa
increase compared to a 2.8 MPa increase. They concluded water potential increases
associated with the wetting of a dry soil may be a major catalyst for soil C turnover. It
can be inferred that a proportional amount of N, based on the C:N ratio of the biomass,
would also release upon cell lysis.
39
Table 2.1 Soil particle size distribution, C and N concentration, C to N ratio, and initial inorganic N concentration Soil Clay Sand Total C Total N C/N Initial inorganic N
------%------ ------mg kg-1------ mg kg-1 Orangeburg 19.6 72.4 3691 380 9.7 9.1 Norfolk 8.5 87.5 4381 322 13.6 1.4 Norfolk depressional 14.3 65.2 12526 753 16.6 13.1
40
Table 2.2 Dry weights, total C and N concentration, C to N ratio, and initial inorganic N concentration of cotton leaves and compost Residues Rate Total C Total N Organic N C/N Initial inorganic N
mg kg-1 -------------g kg-1------------- mg kg-1 cotton leaves 2057 432.3 29.0 28.4 14.9 570.5 compost 15000 240.1 14.2 13.2 16.9 958.6
41
Table 2.3 Net N mineralization after 185 days of incubation for the three study soils and treatments Soil and moisture regime Leaves Compost Control
% of applied N mg kg-1 Orangeburg, constant moisture 25.72 4.86 16.09 Orangeburg, wet and dry -1.28 1.59 18.32 Norfolk, constant moisture 28.45 3.78 23.10 Norfolk, wet and dry 2.04 1.69 21.02 Norfolk depressional, constant moisture 39.53 9.31 46.53 Norfolk depressional, wet and dry 6.85 3.25 40.32 LSD (a = 0.05) for moisture regime 9.56 2.71 6.45 LSD (a = 0.05) for soil type N.S. N.S. 5.29
42
Table 2.4 GLM Table for N mineralized as % N applied as residue. α=0.05 Source df SS MS F Pr > F soil 2 335.282 167.641 3.97 0.0294 moisture 1 2377.327 2377.327 56.36 <0.0001
residue 1 1475.156 1475.156 34.97 <0.0001 moisture x residue 1 1393.514 1393.514 33.04 <0.0001
error 30 1265.487 42.183
Total 35 6846.766
43
Norfolk Norfolk depressional
Figure 2.1 Cumulative N mineralized from the control soils with no residue.
Orangeburg
Time (days)0 50 100 150 200
N m
iner
aliz
ed (m
g kg
-1)
0
10
20
30
40
50
60
Time (days)0 50 100 150 200
N m
iner
aliz
ed (m
g kg
-1)
0
10
20
30
40
50
60
Time (days)0 50 100 150 200
N m
iner
aliz
ed (m
g kg
-1)
0
10
20
30
40
50
60
constant moisturewet and dryzero
44
Norfolk Orangeburg
Figure 2.2 Nitrogen mineralized as % of N applied as cotton leaves or compost under
Time (days)0 50 100 150 200
N m
iner
aliz
ed (%
of a
pplie
d N
)
-20
0
20
40
Time (days)0 50 100 150 200
N m
iner
aliz
ed (%
of a
pplie
d N
)
-20
0
20
40
compost, constant moisturecompost, wet and drycotton leaves, constant moisturecotton leaves, wet and dryzero
Time (days)0 50 100 150 200
N m
iner
aliz
ed (%
of a
pplie
d N
)
-20
0
20
40
Norfolk depressional
different moisture regimes.
45
Figure 2.3 Plot of least squared means x moisture. The symbol is residue value. Wide
Moisture Regimeconstant moisture wet and dry
N m
iner
aliz
ed (
% o
f app
lied
N)
0
5
10
15
20
25
30
35
compostcotton leaves
gaps between values represent significant differences between treatment variables.
46
Figure 2.4 Total soluble C extracted from Norfolk soils with cotton leaves to evaluate
Norfolk + cotton leaves
Tota
l sol
uble
C (m
g C
kg-1
soil)
0
5
10
15
20
25
constant moisturewet and dry20.44
14.08
whether treatments that underwent repeated wetting and drying experienced denitrification. Less total soluble C in the wet and dry treatment was an indication that denitrification had not occurred.
47
THE EFFECT OF WETTING AND DRYING ON CARBON MINERALIZATION
Introduction
Carbon mineralization rates in soils are dependent on a number of factors, including
soil moisture, temperature, texture, microbial populations, and residue composition and
placement. Researchers have studied the effect drying and rewetting has on C
mineralization rates to determine whether it differs significantly from soils maintained at
a constant moisture content. Soils in the field do not stay at a constant moisture level, but
fluctuate according to environmental conditions. Birch (1958) found drying and
rewetting released a flush of mineralized C, though the amount mineralized decreased
after each successive rewetting episode. Wet-dry cycles also affected amounts of
dissolved organic carbon measured in soils, according to Lundquist et al. (1999).
The purpose of this experiment was to determine the effect frequent drying and
rewetting had on C mineralization rates of soil organic matter and cotton leaf or compost
residues, in coastal plain soils of the southeastern United States.
Materials and Methods
Three soil samples were collected from the upper 0.15 m of a field under
conventional tillage in the coastal plain of Georgia to provide a range of clay and soil
organic matter contents. The Norfolk loamy sand (coarse-loamy, kaolinitic, thermic
Typic Kandiudults) contained both the lowest clay percentage and the lowest soil organic
48
matter. The Orangeburg sandy loam (fine-loamy, kaolinitic, thermic Typic Kandiudults)
contained the highest clay content and the medium level of soil organic matter of the
selected soils. The Norfolk depressional sandy loam (fine-loamy, kaolinitic, thermic
Arenic Kandiudults), a taxadjunct to the Norfolk series, contained a medium clay level
and the highest soil organic matter content of the three soils (Table 2.1). Soils were air
dried in the laboratory, crushed, then sieved through a 2-mm sieve to remove small rocks
and non-decayed crop residue, which constituted less than 1% of the soil by weight. The
water content of the soils at field capacity (–0.01 MPa) was determined by using a
pressure chamber. Three replicates of each soil were placed into steel cores with a 2-cm
radius and 0.9-cm height and saturated with deionized water at atmospheric pressure. The
samples were placed into the pressure chamber (Soil Moisture Equipment Co., Santa
Barbara, CA) and brought to –0.01 MPa, weighed, dried in an oven at 105 oC for 48
hours, then weighed again (Klute, 1986). A subsample of each soil was analyzed for C
and N with a Carlo-Erba NA 1500 Analyzer for Carbon and Nitrogen, Milan, Italy,
according to the methods described by Kirsten (1983).
The study treatment design was a factorial experiment of three soils (Norfolk,
Orangeburg, Norfolk Depressional), three residues (none, cotton leaves, compost) and
two soil water levels (constant wet and alternating wet and dry). Organic residues chosen
for the study were cotton leaves and compost. The compost selected began as a mixture
of grass clippings, hardwood leaves, and pine needles. Windrows were stacked 120 cm
high and mixed until the materials went through a peak heat. Both residues were oven-
dried at 105o C for 96 hours. Samples were then sieved in a 2-mm sieve, composited, and
ball milled. A subsample was analyzed for C and N (Table 2.2) with a Carlo-Erba NA
49
1500 Analyzer for Carbon and Nitrogen, Milan, Italy (Kirsten, 1983) by dry micro-
Dumas combustion. Cotton leaves were applied at 2057 mg kg-1 soil, and compost was
applied at 15000 mg kg-1 soil. After placement of a 0.45-µm Supor® 450membrane filter
(Gelman Sciences, Ann Arbor, MI) filter in the bottom of a buchner funnel, residues were
mixed with soils by placing the weighed soil and residue into the buchner funnel, then
stirring with a glass rod for 5 min. Soil that fell through the bottom of the buchner funnel
was captured by placing the funnel on paper during stirring, then pouring the soil back
into the buchner funnel. There were three replicates of all treatments.
Treatments were divided into two systems. Those maintained at field capacity for
the duration of the study were kept in an aquarium (25.5 x 50 x 30.5cm) whose external
surface was taped with black duct tape to prevent algae growth. The bottom 2 cm of the
tank held deionized water to help maintain high humidity. The top of the tank was
covered by a stainless steel lid with 4-mm entry and exit ports. Air was pumped in by
means of two Second Nature® Challenger 1™ aquarium air pumps providing 4L min-1
air through Tygon® tubing into the bottom of a carboy partially filled with 4L deionized
water. Moisture saturated air then exited through the top of the carboy via Tygon tubing
into the entry port for the tank. Treatments that were dried and rewetted were stored in
the high humidity tank for 3 d, then transferred to an identical tank that had laboratory air
pumped into a dry glass bottle which then flowed into the entry port of the stainless steel
lid. The bottom of the dry tank contained no water, but instead held 454-g Drierite®
(W.A. Hammond Drierite Co., Xenia, OH) anhydrous calcium sulfate, that was changed
daily. Soils were dried down in this tank for 11 d before being rewetted. Temperature
and moisture levels inside the tanks were recorded for both treatments two times per
50
week. Each treatment was brought to field capacity with deionized water, then incubated
either at a constant humidity of ~98% RH throughout the experiment, or incubated at
~98% RH for 3 d, then transferred to the dry tank for 11 d.
Carbon dioxide levels were determined daily for the first 48 hours after rewetting,
then on an approximately every-other-day basis, by sealing the bottom of the porous
Buchner funnel with Saran® Wrap, then recording the time the treatment was sealed.
The seal was obtained by laying the pre-cut Saran square over the Buchner funnel
bottom, then pressing the flanged Buchner funnel top firmly into the Buchner funnel
bottom. The top was sealed by a flanged poly-vinyl chloride (PVC) disk with a rubber
O-ring, pressed firmly into the Buchner funnel top. The PVC lid had a rubber septum
fitted into the middle of the lid that allowed for CO2 extraction by syringe. After waiting
approximately one hour, the needle of a 2-mL syringe was inserted, plunger depressed,
into the headspace of the treatment. The plunger was pulled to 2 mL, then depressed five
times to circulate the air trapped in the soil pore space. Then 2 mL of headspace air was
extracted and injected into a 2-mL glass vial with a septum lid. The CO2 extraction time
was recorded. Lids and Saran wrap were immediately removed from the treatments,
following CO2 extractions. All glass vials were sealed out-of-doors between 1900 and
2200 hours to ensure consistent background CO2 levels, and after injection, stored at 4o C
until analysis. The headspace for each treatment was determined by measuring the
distance from the top of the soil treatment to the top of the Buchner funnel top, then
subtracting the depth of the PVC lid flange. The diameter of each Buchner funnel was
measured. Bulk densities (ρb) of each treatment were measured and used to calculate
porosity based on an assumed particle density (ρs) of 2.65 g mL-1. The predominate
51
particles are quartz. Porosity was calculated as: 1 - (ρb/ρs). Relative air porosity was then
calculated by subtracting the portion of total porosity occupied by liquid (1g = 1mL).
Because some soil was lost by leaching, we needed to know the amount of oven dry soil
in the buchner funnel at each CO2 measurement. Using the air dry weight (g) taken on
day 210, and the oven dry weight taken on day 213 (at the end of the experiment when
this could be measured), the oven dry weight for each day was calculated by:
Weight of oven dry soil on day Zn = weight of air dry soil on day Zn – (air dry weight day
210 – oven dry weight day 213) [2.1]
Where Zn represents the leaching day, and n varies from 1 to 13, e.g. Z1 = day 14, Z2 =
day 32, etcetera.
This relative air porosity was added to the head space above the soil to reach total
head space (mL). CO2 was analyzed on a Varian Star 3600CX (Varian Analytical
Instruments, Sugar Land, Texas) gas chromatograph, which determined concentration
based on thermal conductivity. CO2-C evolution rate was calculated by the equation:
µg CO2-C g-1soil x hr = % CO2 in sample x (4.95702 µg CO2-C/mL) x mL headspace
[2.2]
based on the equation to calculate a 1% CO2 standard. Since there are 0.0413091 mol
CO2 per L CO2 at 22o C, and 12 x 106 µg CO2-C per mol CO2, a 1% CO2 standard
contains 4.957092 µg CO2-C per ml according to the following equation:
52
(1mL CO2/100mL std) x (0.0413091 mol CO2*/ L CO2) x (1 L CO2/1000mL CO2) x
(12x106 µg CO2-C/mol CO2) = 4.957092 µg CO2-C/mL standard. [2.3]
* at 22o C.
Results and Discussion
For all control soils (those without residue), the Orangeburg soil maintained at
constant moisture mineralized the most C at 493.3 mg kg-1 at 185 d. The Norfolk soil at
constant moisture mineralized the least C at 257.4 mg kg-1 at 185 d although it was
statistically identical to the Norfolk subjected to repeated wetting and drying that
mineralized 258.8 mg kg-1 (Figure 3.1). Analyzed by moisture treatment, the Norfolk
and Norfolk depressional mineralized similar amounts of C, but the Orangeburg
treatment that was repeatedly dried and rewetted mineralized 57% of the treatment under
constant moisture. By itself, moisture was not significant in determining mineralized C
at the α=0.05 level (p value = 0.0636). Soil type, by itself, was significant at the α=0.05
level, (p value = 0.0088). There was a significant interaction between soil x moisture at
the α=0.05 level (p value = 0.0034), therefore soil type and moisture were retained in the
statistical model. Coefficient of variation rates averaged 42% with a range from 4% to
138% within replicates of treatments. The Orangeburg and Norfolk depressional tended
to mineralize more C sooner than the Norfolk soil. By 32 d, the Orangeburg had
mineralized between 41.8 and 46.5% of the total mineralized C at 185 d, depending on
moisture treatment (Figure 3.2). Similarly, by 32 d, the Norfolk depressional had
53
mineralized between 39.0 and 46.3% of the total mineralized C. By constrast, the
Norfolk mineralized from 24.9 to 27.7% of the total C mineralized, by 32 d. The Norfolk
soil initially contained more C than the Orangeburg, but is a loamy sand, while the
Orangeburg is a sandy loam. The Norfolk tended to dry more quickly than the
Orangeburg, as was noted by visual observation during the experiment, and therefore
spent a larger percentage of the time during the experiment in a “dry” state. A
preliminary study conducted as described in Chapter 1 revealed the Norfolk lost water
content (from field capacity to air-dry) in 85% of the time as the Orangeburg (Figure
1.1). This may help explain reduced mineralization for the treatment undergoing
repeated wetting and drying, but does not explain the treatment maintained at constant
moisture. In fact, previous researchers found clay particles provided a “protective effect”
for microorganisms, resulting in lower rates of N mineralization for soils with higher clay
contents ( Birch 1958; Sorensen 1981; van Veen et al. 1985; Ladd et al. 1992), but that
the influence of texture may be less important for C mineralization (Hassink et al. 1993;
Hassink et al. 1994). In a study on N mineralization, Strong et al. (1999) observed that
when soils were treated with clover-derived substrate, clay increased N mineralization
and nitrification rates. They state that this may have been because clay limited the
diffusion of partially decomposed organics (i.e. C-based compounds) away from the
decomposing microbial population, thereby helping to facilitate more complete
decomposition of the organic material. If C-based compounds are more limited in
diffusion away from the decomposing microbial population, one would expect higher
rates of CO2 production as C is more completely mineralized.
54
For all soils treated with cotton leaves, the Norfolk depressional under constant
moisture and under repeated wetting and drying, as well as the Orangeburg soil under
constant moisture released the most CO2 (681, 685, and 674 mg kg-1, respectively). The
Norfolk soil with cotton leaves under repeated wetting and drying released the least CO2
over the study (437 mg kg-1) but was similar to the Orangeburg under wetting and drying
at 467 mg kg-1. Although the initial application rate of C from cotton leaves was 24.7%
of the application rate for C from compost (Table 2.1), in all cases treatments with cotton
leaves mineralized more C than treatments with compost for a given soil (Figure 3.1).
The Orangeburg with cotton leaves under constant moisture mineralized 41.8% of
total C mineralized, after 32 d. The Orangeburg with cotton leaves under wetting and
drying mineralized 59.9% after 32 d. The Norfolk soil with cotton leaves under constant
moisture mineralized 52.2% after 32 d, and the Norfolk soil with cotton leaves under
wetting and drying mineralized 57.7% after 32 d. The Norfolk depressional with cotton
leaves under constant moisture mineralized 53.5% after 32 d, and the Norfolk
depressional with cotton leaves under wetting and drying mineralized 52.7% after 32 d.
Across soils and moisture treatments, roughly half the C mineralized as CO2 after 185 d
had mineralized after the first month.
For all soils with compost, the Orangeburg under constant moisture mineralized the
most C as CO2, at a mean value of 592-mg kg-1. The Orangeburg under wetting and
drying, on average, mineralized the least C at 330-mg kg-1. By contrast the Norfolk and
Norfolk depressional soils under different moisture treatments mineralized similar
amounts of C (Figure 3.1).
55
When mineralized C is evaluated in terms of percent C applied, certain distinct
patterns emerge (Figure 3.3). Means and standard deviations were obtained by
subtracting the mean value of the control soil mineralized C from each replication of the
soil plus residue mineralized C value, then dividing the differences by the amount of
initial C applied, and multiplying by 100. In a few instances in the Orangeburg soil, the
treatments with residue evolved less CO2 than the mean value of CO2 evolved from the
control soil, resulting in a negative slope (Figure 3.3).
Soil type was significant at the α = 0.05 level, as was type of residue. Statistical
analysis using Tukey’s method revealed the Norfolk depressional and Orangeburg were
significantly different (Table 2.3). Moisture was not significant, nor were any
interactions between variables.
Residue type played an important role in the amount of C mineralized. Cotton
leaves mineralized between 20.3% and 37.9% (mean values) of their C content after 185
d, depending on the soil type and moisture treatment (Figure 3.3). Compost, by contrast,
mineralized between 0.7% and 6.15% of their C content (mean values) after 185 d
(Figure 3.3). In cotton leaves, C underwent rapid mineralization, with over half the total
C mineralized by 32 d, with the exception of the Orangeburg soil under constant moisture
(Figure 3.3). In the case of the Norfolk soil under repeated wetting and drying, 93% of
the C mineralized had mineralized after 32 d. This rapid mineralization is supported by
observed N immobilization in soils with cotton leaf residues during the first 14 to 32 d as
shown in Chapter 2.
56
Compost showed very little C mineralization. The material underwent thorough
decay prior to use in the experiment, leaving humic materials that were apparently more
resistant to decomposition. The C mineralization data are consistent with the N data for
soil with compost in Chapter 2, which also showed very little mineralization (Figure 2.5).
57
Figure 3.1 Total mean integrated CO2-C after 185 d from the three selected soils at
Orangeburg
CO
2-C
(mg
kg-1
)
0
200
400
600
800
Norfolk
CO
2-C
(mg
kg-1
)
0
200
400
600
800
Norfolk depressional
CO
2-C
(mg
kg-1
)
0
200
400
600
800
constant moisture: soilconstant moisture: soil + compostconstant moisture: soil + cotton leaveswet and dry: soilwet and dry: soil + compostwet and dry: soil + cotton leaves
257
418
506
259
386
437
326
504
681
390
578
685
493
592
674
281330
467
various combinations of moisture regimes and residue types.
58
Figure 3.2 Mean cumulative CO2-C in the three control soils with no residue
Orangeburg
Time (days)0 50 100 150 200
Cum
ulat
ive
CO
2-C
(mg
kg-1
)
0
100
200
300
400
500
600
Norfolk
Time (days)0 50 100 150 200
Cum
ulat
ive
CO
2-C
(mg
kg-1
)
0
100
200
300
400
500
600
Norfolk depressional
Time (days)0 50 100 150 200
Cum
ulat
ive
CO
2-C
(mg
kg-1
)
0
100
200
300
400
500
600
constant moisturewet and dry
applied, by moisture regime.
59
Figure 3.3 Cumulative CO2-C, evolved from cotton leaves or compost, by moisture
Orangeburg
Time (days)0 50 100 150 200
Cum
ulat
ive
CO
2-C
(% C
app
lied)
-10
0
10
20
30
40
50
60
cotton leaves, constant moisturecotton leaves, wet and drycompost, constant moisturecompost, wet and dryzero
Norfolk
Time (days)0 50 100 150 200
Cum
ulat
ive
CO
2-C
(% C
app
lied)
0
20
40
60
Norfolk depressional
Time (days)0 50 100 150 200
Cum
ulat
ive
CO
2-C
(% C
app
lied)
-10
0
10
20
30
40
50
60
regime.
60
REFERENCES
Adu, J.K., and J.M. Oades. 1978. Physical factors influencing decomposition of organic materials in soil aggregates. Soil Biology and Biochemistry 10: 109-115.
Appel, T., and K. Mengel. 1993. Nitrogen fractions in sandy soils in relation to plant
nitrogen uptake and organic matter incorporation. Soil Biology and Biochemistry 25: 685-691.
Baldwin, D.S., and A.M. Mitchell. 2000. The effects of drying and re-flooding on the
sediment and soil nutrient dynamics of lowland river-floodplain systems: a synthesis. Regulated Rivers: Research and Management 16: 457-467.
Beare, M.H., M.L. Cabrera, P.F. Hendrix, and D.C. Coleman. 1994. Aggregate-protected
and unprotected organic matter pools in conventional- and no-tillage soils. Soil Science Society of America Journal 58: 787-795.
Birch, H.F., and M.T. Friend. 1956. Humus decomposition in East African soils. Nature
178: 500. Birch, H.F., 1958. The effect of soil drying on humus decomposition and nitrogen
availability. Plant and Soil 10: 9-31. Birch, H.F., 1959. Further observations on humus decomposition and nitrification. Plant
and Soil 11: 262-286. Birch, H.F., 1960. Nitrification in soils after different periods of dryness. Plant and Soil
12: 81-96. Bloem, J., P.C. de Ruiter, G.J. Koopman, G. Lebbink, and L. Brussaard. 1992. Microbial
numbers and activity in dried and rewetted arable soil under integrated and conventional management. Soil Biology and Biochemistry 24: 655-665.
Cabrera, M.L., 1993. Modeling the flush of nitrogen mineralization caused by drying and
rewetting soils. Soil Science Society of America Journal 57: 63-66. Cabrera, M.L., and D.E. Kissel. 1988b. Evaluation of a method to predict nitrogen
mineralization from soil organic matter under field conditions. Soil Science Society of America Journal 52: 1027-1031.
Cameron, R.S., and A.M. Posner. 1979. Mineralisable organic nitrogen in soils
fractionated according to particle size. Journal of Soil Science 30: 565-577.
61
Castellanos, J.Z., and P.F. Pratt. 1981. Mineralization of manure nitrogen-correlation
with laboratory indexes. Soil Science Society of America Journal 45:354-357. Chichester, F.W., 1969. Nitrogen in soil organo-mineral sedimentation fractions. Soil
Science 5: 356-363. Constantinides, M., and J.H. Fownes. 1994. Nitrogen mineralization from leaves and
litter of tropical plants: relationship to nitrogen, lignin and soluble polyphenol concentrations. Soil Biology and Biochemistry 26: 49-55.
Cook, B.D., and D.L. Allan. 1992a. Dissolved organic carbon in old field soils: total
amounts as a measure of available resources for soil mineralization. Soil Biology and Biochemistry 24: 585-594.
Cook, B.D., and D.L. Allan. 1992b. Dissolved organic carbon in old field soils:
compositional changes during the biodegradation of soil organic matter. Soil Biology and Biochemistry 24: 595-600.
Cortez, J., 1989. Effect of drying and rewetting on mineralization and distribution of
bacterial constituents in soil fractions. Biology and Fertility of Soils 7: 142-151. Craswell, E.T., P.G. Saffigna, and S.S. Waring. 1970. The mineralization of organic
nitrogen in dry soil aggregates of different sizes. Plant and Soil 33: 383-392. Craswell, E.T., and S.A. Waring. 1972a. Effect of grinding on the decomposition of soil
organic matter-I. The mineralization of organic nitrogen in relation to soil type. Soil Biology and Biochemistry 4: 427-433.
Craswell, E.T., and S.A. Waring. 1972b. Effect of grinding on the decomposition of soil
organic matter-II. Oxygen uptake and nitrogen mineralization in virgin and cultivated cracking clay soils. Soil Biology and Biochemistry 4: 435-442.
Curtin, D., F. Selles, H. Wang, C.A. Campbell, and V.O. Biederbeck. 1998. Carbon
dioxide emissions and transformation of soil carbon and nitrogen during wheat straw decomposition. Soil Science Society of America Journal 62: 1035-1041.
Das, S.K., G.S. Reddy, K.L. Sharma, K.P.R. Vittal, B. Venkateswarlu, M.N. Reddy, and
Y.V.R. Reddy. 1993. Prediction of nitrogen availability in soil after crop residue incorporation. Fertilizer Research 34: 209-215.
De Bruin, B., F.W.T. Penning De Vries, L.W. Van Broekhoven, N. Vertregt, and S.C.
Van de Geijn. 1989. Net nitrogen mineralization, nitrification and CO2 production in alternating moisture conditions in an unfertilized low-humus sandy soil from the Sahel. Plant and Soil 113: 69-78.
62
De Haan, S. 1981. Results of municipal waste compost research over more than fifty years at the Institute for Soil Fertility at Haren Groningen, the Netherlands. Netherlands Journal of Agricultural Science 29:49-61.
De Neve, S., and G. Hofman. 1996. Modelling N mineralization of vegetable crop
residues during laboratory incubations. Soil Biology and Biochemistry 28:1451-1457.
Edwards, A.P., and J.M. Bremner. 1967. Microaggregates in soils. Soil Science 18: 64-
73. Egelkraut, T.M., D.E. Kissel, and M.L. Cabrera. 2000. Effect of soil texture on nitrogen
mineralized from cotton residues and compost. Journal of Environmental Quality 29:1518-1522.
Elliot, E.T., 1986. Aggregate structure and carbon, nitrogen and phosphorus in native and
cultivated soils. Soil Science Society of America Journal 50: 627-633. EPA. March, 1984. Methods for chemical analysis of water and wastes. EPA-600/4-79-
020. “Nitrogen, Ammonia” Method 350.1 (Colorimetric, Automated Phenate) Storet No. Total 00610, Dissolved 00608.
Eriksen, G.N., Coale, F.J., and G.A. Bollero. 1999. Soil nitrogen dynamics and maize
production in municipal solid waste amended soil. Agronomy Journal 91: 1009-1016.
Fox, R.H., R.J.K Myers, and I. Vallis. 1990. The nitrogen mineralization rate of legume
residues in soil as influenced by their polyphenol, lignin, and nitrogen contents. Plant and Soil 129:251-259.
Frankenberger, W.T., and H.M Abdelgamid. 1985. Kinetic parameters of nitrogen
mineralization rates of leguminous crops incorporated into soil. Plant and Soil 87:257-271.
Franzluebbers, K., R.W. Weaver, A.S.R. Juo, and A.J. Franzleubbers. 1994. Carbon and
nitrogen mineralization from cowpea plants part decomposing in moist and in repeatedly dried and wetted soil. Soil Biology and Biochemistry 26: 1379-1387.
Franzleubbers, K., Weaver, R.W., Juo, A.S.R., and A.J Franzleubbers. 1995.
Mineralization of carbon and nitrogen from cowpea leaves decomposing in soils with different levels of microbial biomass. Biology and Fertility of Soils 19: 100-102.
63
Frink, C.R., Waggoner, P.E., and J.H. Ausubel. 1999. Nitrogen fertilizer: Retrospect and prospect. Proceedings of the National Academy of Sciences, USA 96: 1175-1180.
Gordillo, R.M., and M.L. Cabrera. 1997. Mineralizable nitrogen in broiler litter-II. Effect
of selected soil characteristics. Journal of Environmental Quality 26: 1679-1686. Greaves, J.E., and E.G. Carter. 1920. Influence of moisture on the bacterial levels of soil.
Soil Science 10:361-385. Greenland, D.J., 1965. Interaction between clays and organic compounds in soils-II.
Adsorption of soil organic compounds and its effect on soil properties. Soils and Fertilizers 28: 521-532.
Gregorich, E.G., R.G. Kachanoski, and R.P Voroney. 1989. Carbon mineralization in soil
size fractions after various amounts of aggregate disruption. Journal of Soil Science 40: 649-659.
Hadas, A., and R. Portnoy. 1994. Nitrogen and carbon mineralization rates of composted
manures incubated in soil. Journal of Environmental Quality 23: 1184-1189. Hayashi, R., and T. Harada. 1969. Characterization of the organic nitrogen becoming
decomposable through the effect of drying of a soil. Soil Science and Plant Nutrition 15: 226-234.
He, X.T., Traina, S.J., and T.J. Logan. 1992. Chemical properties of municipal solid
waste composts. Journal of Environmental Quality 21: 318-329. Herlihy, M., 1979. Nitrogen mineralisation in soils of varying texture, moisture and
organic matter-I. Potential and experimental values in fallow soils. Plant and Soil 53: 255-267.
Hiura, K., T Hattori, and C. Furusaka. 1976. Bacterialogical studies on the mineralization
of organic nitrogen in paddy soils–I. Effects of mechanical disruption of soils on ammonification and bacterial number. Soil Science and Plant Nutrition 22: 459-465.
Jager, G., and E.H. Bruins. 1975. Effect of repeated drying at different temperatures on
soil organic matter decomposition and characteristics, and on the soil microflora. Soil Biology and Biochemistry 7: 153-159.
Jenkinson, D.S., 1966a. The priming action. In The use of isotopes in soil organic matter
studies. Pergamon Press, Oxford:199-208. Kieft, T.L., E. Soroker, and M.K. Firestone. 1987. Microbial biomass response to a rapid
increase in water potential when dry soil is wetted. Soil Biology and Biochemistry 19: 119-126.
64
Kirchmann, H., and R. Bergqvist. 1989. Carbon and nitrogen mineralization of white
clover plants (Trifolium repens) of different age during aerobic incubation with soil. Zeitschrift für Pflanzenernährung und Bodenkunde 152:281-286.
Kirsten, W., 1983. Organic elemental analysis: ultramicro, micro, and trace methods.
Academic Press, Harcourt Brace Jovanovich, New York. Klute, A., 1986. Water Retention, Laboratory methods, in Physical and Mineralogical
Methods, Klute, A., Editor. American Society of Agronomy, Madison, WI. 643. Kuikman, P.J., A.G. Jansen, and J.A. Van Veen. 1991. 15N-nitrogen mineralization from
bacteria by protozoan grazing at different soil moisture regimes. Soil Biology and Biochemistry 23: 193-200.
Ladd, J.N., and M Amato. 1988. Relationships between biomass 14C of a range of
fumigated soils. Soil Biology and Biochemistry 20: 115-116. Ladd, J.N., J.M. Oades, and M. Amato. 1981. Microbial biomass formed from 14C, 15N
labelled plant material decomposing in soils in the field. Soil Biology and Biochemistry 13: 119-126.
Legg, J.O., F.W. Chichester, G. Stanford, and W.H. De Mar. 1971. Incorporation of 15N-
tagged mineral nitrogen into stable forms of soil organic nitrogen. Soil Science Society of America Proceedings 35: 273-276.
Lundquist, E.J., L.E. Jackson, and K.M. Scow. 1999b. Wet-dry cycles affect dissolved
organic carbon in two California agricultural soils. Soil Biology and Biochemistry 31: 1031-1038.
Marumoto, T., H. Kai, T. Yoshida, and T. Harada. 1977a. Relationship between an
accumulation of soil organic matter becoming decomposable due to drying of soil and microbial cells. Soil Science and Plant Nutrition 23: 1-8.
Marumoto, T., H. Kai, T. Yoshida, and T. Harada. 1977b. Drying effect on
mineralizations of microbial cells and their cell walls in soil and contribution of microbial cell walls as a source of decomposable soil organic matter due to drying. Soil Science and Plant Nutrition 23: 9-19.
McKeague, J.A. 1971. Organic matter in particle-size and specific gravity fractions of
some Ah horizons. Canadian Journal of Soil Science 51: 499-505. Merckx, R., A. Den Hertog, and J.A. Van Veen. 1985. Turnover of root-derived material
and related microbial biomass formation in soils of different texture. Soil Biology and Biochemistry 17: 565-569.
65
Müller, M.M., V. Sundman, O. Soininvaara, and A. Meriläinen. 1988. Biology and
Fertility of Soils 6: 78-83. Mullins, G.L., and C.H. Burmester. 1990. Dry matter, nitrogen, phosphorus, and
potassium accumulation by four cotton varieties. Agronomy Journal 82: 729-736. Myers, R.J.K., C.A. Campbell, and K.L. Weir. 1982. Quantitative relationship between
net nitrogen mineralization and moisture content of soils. Canadian Journal of Soil Science 62:11-124.
Navarro, M., Pujolà, M., Soliva, M., and Mª A. Garau. 1992. Nitrogen mineralization
study in compost. Acta Horticulturae 302: 279-294. Nielsen, D.R., and J.W. Biggar. 1961. Miscible displacement in soils: I. Experimental
information. Soil Science Society of America Proceedings 25: 1-5. Oades, J.M., 1988. An introduction to organic matter in mineral soils. In Minerals in Soil
Environments. 2nd ed., Soil Science Society of America, Madison: 89-159. Oglesby, K.A., and J.H. Fownes. 1992. Effects of chemical composition on nitrogen
mineralization from green manures of seven tropical leguminous trees. Plant and Soil 143: 127-132.
Palm, C.A., and P.A Sanchez. 1991. Nitrogen release from the leaves of some tropical
legumes as affected by their lignin and polyphenolic contents. Soil Biology and Biochemistry 23: 83-88.
Pilbeam, C.J., B.S. Mahapatra, and M. Wood. 1993. Soil matric potential effects on gross
rates of nitrogen mineralization in an orthic ferralsol from Kenya. Soil Biology and Biochemistry 25: 1409-1413.
Powers, R.F., 1990. Nitrogen mineralization along an altitudinal gradient: interactions of
soil temperature, moisture, and substrate quality. Forest Ecology and Management 30: 19-29.
Quemada, M., and M.L. Cabrera. 1997. Temperature and moisture effects on C and N
mineralization from surface applied clover residue. Plant and Soil 189: 127-137. Russell, J.C., E.G. Jones, and G.M. Bahrt. 1925. The temperature and moisture factors in
nitrate production. Soil Science 19:381-398.
SAS Institute. 1985. SAS user’s guide: Statistics. Version 6 ed. SAS Institute, Inc., Cary, NC.
66
Seneviratne, R., and A. Wild. 1985. Effect of mild drying on the mineralization of soil nitrogen. Plant and Soil 84: 175-179.
Sierra, J., 1997. Temperature and soil moisture dependence of N mineralization in intact
soil cores. Soil Biology and Biochemistry 29: 1557-1563. Sikora, L.J., and V. Yakovchenko. 1996. Soil organic matter mineralization after compost
amendment. Soil Science Society of America Journal 60: 1401-1404. Sørensen, L.H., 1974. Rate of decomposition of organic matter in soil as influenced by
repeated air drying-rewetting and repeated additions of organic material. Soil Biology and Biochemistry 6:287-292.
Sørensen, L.H., 1983a. Size and persistence of the microbial biomass formed during the
humification of glucose, hemicellulose, cellulose, and straw in soils containing different amounts of clay. Plant and Soil 75: 121-130.
Sørensen, L.H., 1983b. The influence of stress treatments on the microbial biomass and
the rate of decomposition of humified matter in soils containing different amounts of clay. Plant and Soil 75: 107-119.
Sørensen, P., and E.S. Jensen. 1995. Mineralization-immobilization and plant uptake of
nitrogen as influenced by the spatial distribution of cattle slurry in soils of different texture. Plant and Soil 173:283-291.
Soulides, D.A., and F.E. Allison. 1961.Effect of drying and freezing soils on carbon
dioxide production, available mineral nutrients, aggregation, and bacterial population. Soil Science 91:291-298.
Stanford, G., and E. Epstein. 1974. Nitrogen mineralization-water relations in soils. Soil
Science Society of America Proceedings 38: 103-107. Stanford, G., M.H. Frere, and D.H Schwaninger. 1973. Temperature coefficient of soil
nitrogen mineralization. Soil Science 115: 321-323. Stanford G., and J. Hanway. 1955. Predicting nitrogen fertilizer needs of Iowa soils -II. A
simplified technique for determining relative nitrate production in soils. Soil Science Society of America Proceedings 19:74-77.
Stanford, G., and S.J. Smith. 1972. Nitrogen mineralization potentials of soils. Soil
Science Society of America Proceedings 36:465-472. Stevenson, I.L., 1956. Some observations on the microbial activity in remoistened air-
dried soils. Plant and Soil 8:170-182.
67
Stark, J.M., and M.K. Firestone. 1995. Mechanisms for soil moisture effects on activity
of nitrifying bacteria. Applied and Environmental Microbiology 61: 218-221. Strong, D.T., P.W.G. Sale, and K.R. Helyar. 1999. The influence of the soil matrix on
nitrogen mineralisation and nitrification- IV. Texture. Australian Journal of Soil Research 37: 329-344.
Tian, G., B.T. Kang, and L. Brussaard. 1992. Effects of chemical composition on N, Ca,
and Mg release during incubation of leaves from selected agroforestry and fallow plant species. Biogeochemistry 16:103-119.
Tisdale, S.L., et al., 1999. Soil fertility and fertilizers: an introduction to nutrient
management. 6th ed., Prentice Hall, Inc., Upper Saddle River, NJ: 108. Tyson, S.C., and M.L. Cabrera. 1993. Nitrogen mineralization in soils amended with
composted and uncomposted poultry litter. Communications in Soil Science and Plant Analysis 24: 2361-2374.
Van Gestel, M., R. Merckx, and K. Vlassak. 1993a. Microbial biomass responses to soil
drying and rewetting: the fate of fast- and slow-growing microorganisms in soils from different climates. Soil Biology and Biochemistry 25: 109-123.
Van Gestel, M., R. Merckx, and K. Vlassak. 1993b. Soil drying and rewetting and the
turnover of 14C-labelled plant residues: first order decay rates of biomass and non-biomass 14C. Soil Biology and Biochemistry 25: 125-134.
Van Schreven, D.A., 1967. The effect of intermittent drying and wetting of a calcareous
soil on carbon and nitrogen mineralization. Plant and Soil 26: 14-32.
Vigil, M.F., and D.E. Kissel. 1991. Equations for estimating the amount of nitrogen mineralized from crop residues. Soil Science Society of America Journal 55:757-761.
Voroney, R.P., E.A. Paul, and D.W. Anderson. 1989. Decomposition of wheat straw and
stabilization of microbial products. Canadian Journal of Soil Science 69: 63-77. Weast, R.C., ed. 1964. Handbook of Chemistry and Physics.45th ed., The Chemical
Rubber Publishing Company, Cleveland, OH: F8, F88. Westerman, P.W., L. M. Safley, Jr., and J.C. Barker. 1988. Available nitrogen in broiler
and turkey litter. Transactions of the American Society of Agricultural Engineers 31:1070-1075.
68
White, J.C., A. Quiñones-Rivera, and M. Alexander. 1998. Effect of wetting and drying on the bioavailability of organic compounds sequestered in soil. Environmental Toxicology and Chemistry 17: 2378-2382.
Young, J.L., and G. Spycher. 1979. Water dispersable soil organic-mineral particles-I.
Carbon and nitrogen distribution. Soil Science Society of America Journal 43: 324-328.
Zagal, E., 1993. Measurement of microbial biomass in rewetted air-dried soil by
fumigation-incubation and fumigation-extraction techniques. Soil Biology and Biochemistry 25:553-559.